Remove useless unary plus.

It's harmless, but might confuse readers.  Seems to have been introduced
in 6bc8ef0b7f1f1df3.  Back-patch, just to avoid cosmetic cross-branch
differences.

Amit Langote

src/backend/utils/init/postinit.c

@@ -456,7 +456,7 @@ InitializeMaxBackends(void)
 
 	/* the extra unit accounts for the autovacuum launcher */
 	MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
-		+max_worker_processes;
+		max_worker_processes;
 
 	/* internal error because the values were all checked previously */
 	if (MaxBackends > MAX_BACKENDS)